Long-term sub-lethal effects of low concentration commercial herbicide (glyphosate/pelargonic acid) formulation in Bryophyllum pinnatum

- Long-term sub-lethal effects of Roundup formulation were studied in B. pinnatum.
- Hormesis was manifested upon chronic low-dose Roundup exposures in B. pinnatum.
- Roundup dose and leaf biomass interaction could explain F1 plantlets' biomass.
- Biomass asymmetry generally increased with increasing sub-lethal Roundup dose.
- Drifted Roundup may promote biomass and vegetative reproduction in B. pinnatum.

Potential long-term (~ 7 months) sub-lethal impacts of soil-applied low levels of Roundup herbicide formulation were investigated in a greenhouse environment using the vegetative clones of succulent non-crop plant model, Bryophyllum pinnatum (Lam.) Oken. An eleven day LC50 (concentration that killed 50% of the plants) was found to be 6.25% (~ 1.25 mg glyphosate/mL and 1.25 mg pelargonic acid/mL combined), and complete mortality occurred at 12.5%, of the field application rate (i.e., ~ 20 mg glyphosate/mL and 20 mg pelargonic acid/mL as active ingredients). While sub-lethal Roundup (1-5%) exposures led to hormesis-characterized by a significant increase in biomass and vegetative reproduction, higher concentrations (≥ 6.25%) were toxic. A significant interaction between Roundup concentrations and leaf biomass was found to influence the F1 plantlets' biomass. Biomass asymmetry generally increased with increasing Roundup concentrations, indicating that plants were more stressed at higher Roundup treatments but within the low-dose regime (≤ 5% of the as-supplied formulation). While leaf apex region demonstrated higher reproduction with lower biomass increase, leaf basal area showed lower reproduction with greater biomass increase, in plantlets. The results suggest long-term exposures to drifted low levels of Roundup in soil may promote biomass and reproduction in B. pinnatum.

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